Telephone system



Margh 23, 1943. s. SANDALLS. JR 2,314,513

TELEPHONE SYSTEM Filed July 11, 1941 i- DIFFERENTIAL k MMW- FIG.

, INVENTOR By G. SANDALLSLJR A Z'TORNEY Patented Mar. 23, 1943 TELEPHONE SYSTEM George Sandalls, Jr., North Tarrytown, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July 11, 1941, Serial No. 401,898

7 Claims.

This invention relates to telephone exchange systems and more particularly to subscribers lines arranged in such a manner that a subscriber may cause his line to be transferred from its normal termination in an exchange to an auxiliary or emergency appearance before an operator in the same or another exchange.

A feature of the invention resides in an auxiliary circuit arrangement associated with the line, intermediate the line and the exchange, and controlled over the line by switching means at a subscribers station whereby the subscriber can disconnect the line from its normal exchange termination and transfer it to a different (emergency) termination before an operator.

The invention will be understood from the following description when read in connection with the accompanying drawing,

Fig. 1 of which shows a line having normal and auxiliary appearances at an operators switchboard, which line and one station thereof are arrangedvin accordance with the present invention; and

Fig. 2 shows the normal termination of the same line at an automatic central oflice.

Referring to Fig. 1 of the drawing, two stations A and B are shown, connected to a line L which extends to the exchange X, to the right of the broken vertical line AA, where it is shown as being normally connected to the left-hand windings of transformer T over the back contacts of ringing relay I.

The upper right-hand windings of transformer T are shown as connected over contacts 2 of relay 3 to the tip spring of switchboard jack 4 and to ground through the right-hand winding of line relay 5, in series with the inner normal contacts of cut-off relay 6. The'lower right-hand winding of transformer T is shownconnected over contact 1 of relay 3 to the normally open contact 8 of relay 9 which contact, when closed, extends the circuit over contacts ll) of relay 3 to the ring spring of jack 4 and to battery in series withthe left-hand winding of line relay and the outer normal contacts of cut-01f relay 6.

The invention will be understood from the following description of the operation of the system. r

In the normal use of line L, any of the stations, either A or B, can call the operator in .the usual manner by removing the receiver from the switchhook thereby closing a circuit to operate relay 9 which can be traced from ground, the lower winding of relay 9, lower winding of relay ll, upper left-hand winding of transformer T,

upper back contacts of ringing relay I, tip conductor of line L, through the transmitter, switchhook contacts and left-hand winding of the station induction coil, ring conductor of the line, lower back contact of relay I, lower left winding of transformer T and upper winding of relays H and 9 to battery. Relay 9 operates in this circuit, but relay ll, being differentially connected, does not operate.

Operation of relay 9 closes its contacts 8 there-' by completing connection of the right-hand windings of transformer T to battery and ground in serieswith the line relay 5, which relay operates to light line lamp l2 due to the fact that the condenser, connected between the righthandwindings of the transformer T, is bridged by a resistance E3, of the order of 500 ohms. Jack 4 and line lamp !2 constitute the normal switchboard appearance line L and the call is answered by an operator in the usual manner, who extends the calling line, as desired.

If the operator desires to call any station on the line L she inserts one end of her cord circuit in jack 4 and connects ringing current over the tip and ring spring to operate relay M which can be traced from the tip and ring of jack 4, contacts 2 of relay 3, upper half of the righthand winding of transformer T, condenser I5 and resistance l3 in parallel, lower right winding of the transformer, contacts I and I6 of relay 3, winding ofrelay I4 and condenser I! to the ring spring of jack 4. Operation of relay [4 causes relay I to operate thereby connecting ringing current to the line L.

Emergency call Now, let us assume, for example, that station B is engaged in a conversation on a connection involving jack 4 and subscriber A, due to an emergency, desires to obtain control of the line for the purpose of making an emergency call.

It will be noted that the subscribers station equipment at A is identical with the other stations on the line except for the addition of a key K which, when operated, causes ground to be connected to wire H3 at the station thereby grounding the tip conductor of the line and, when the subscribers receiver is removed from the hook, also connecting ground to the ring conductor in series with the station transmitter, contacts 29 of the switchhook, and winding 21 of the induction coil.

When the subscriber at station A, removes his receiver from the hook and actuates key K, the windings of differential relay II are unbalanced, due to the ground at the calling station, andthis relay operates thereby completing an obvious circuit to operate relay 3, which circuit serially includes device 22, which has a high initial resistance to delay operation of relay 3 for a short interval of time thereby obviating false operations of relay H due to line surges, thereby operating relay 3 and causing a false transfer. Device 22, however, rapidly decreases in resistance due to the passage of current therethrough and relay 3 operates thereby opening its contacts 2 and l and disconnecting. the line circuit from lack and closing its contacts 29 and 30, thus causing the line to be transferred to the emergency line circuit L2, appearing in jack 23, which may be before the same or another operator, whereupon line relay 24 operates and causes line lamp 25 to light, which lamp may be of some characteristic color, such as red. When, relay 3 operates, it closes its contact 26 thereby shunting device 22 and allowing it to restore to its normal high resistance condition.

Operation of relay 3 also closes its contacts 21 and 28 thereby completing a holding circuit for itself under control of contacts 8 of relay 9, which relay is operated as long as a receiver remains off the hook at any of the stations, including station A.

When an operator answers by inserting a plug in jack 23, the calling subscriber requests the desired extension of the line.

It will be understood that although the line L has been shown as terminating in a manual exchange, it may terminate in the line circuit of an automatic exchange, as shown in Fig. 2, in which case the stations on the line L will be equipped with pulse transmission devices, such as dials,

mally terminates in a cross-bar ofiice, in order to" avoid a false trouble indication in case a call is extended to the line circuit Ll while the line L is transferred to the emergency line circuit L2.

While line L has been shown as having a plurality of stations, i. e., A and B, and the invention described as a means of obtaining control o the line by station A in case the line is busy, it will be understood that the line may have only a single station, A, which is equipped with an emergency key K in order that emergency calls from that station may be extended to a difierent operator from the one normally answering the line lamp I2. For example, the emergency lamp signal 25 and jack 23 may be located before a toll operator whereas lamp I2 and jack 4 appear before a local operator.

What is claimed is:

1. In a telephone system, an exchange, a subscribers station, a line between said station and said exchange having a normal and also an emergency termination at said exchange, means associated with said line responsive to normal closure of the line at the station to cause said line to be extended to its normal termination, switching means at the station adapted when operated to connect ground to one side of the line, and means responsive to the joint operation of said switching means and closure of said line at the station to disconnect said line from its normal termination and transfer the line to its emergency termination.

2. In a telephone system, an exchange, a subscribers station, an emergency switch thereat, a line between said station and said exchange having a normal and an emergency termination at said exchange, means associated with said line responsive to normal closure of the line at the station to'cause said line to be extended to its normal termination, and means responsive to joint operation of said emergency switch and a line closure at the station to transfer said line from its normal to its emergency termination.

3. In a party line telephone system, an exchange, a plurality of stations, a line interconnecting said stations extending to said exchange and having normal and emergency terminations thereat, emergency switching means at one of said stations, means associated with said line responsive to normal closure of said line at any of said stations to extend said line to its normal termination, and other means responsive to joint operation of said emergency switching means and a line closure at any of said stations to transfer said line from said normal termination to said emergency termination.

4. In a party line telephone system, an exchange, a plurality of stations, a line interconnecting said stations extending to said exchange, a first means associated with said line responsive to normal closure of said line in any one of said stations to extend the line to its normal termination, another means responsive to operation of said emergency switching means to transfer said line from. said normal termination to its emergency termination, said first means being thereafter effective during said normal closure of said line at any station to maintain said line transfer to the emergency termination independent of said other means.

5. In a telephone system, a subscribers station, an exchange, a line therebetween having normal and emergency terminations at said exchange, means associated with said line responsive to the normal operation of the subscribers station equipment in signaling the exchange to extend said line to its normal termination, and means responsive to the connection of ground to both sides of said line to disconnect said line from its normal termination and transfer it to the emergency termination.

6. In a telephone system, a subscribers station, an exchange, a line therebetween, said line being adapted to be terminated in said exchange in either of two line circuits, means associated with said line responsive to a normal closure of said line at said station fortermin'ating th line to one of said line circuits, and other means'asSQ- ciated with said line controlled thereover from said station for transferring said line to the other line circuit.

7. In a common battery telephone system, a subscribers station, an exchange, a line interconnecting said station and exchange, a normal appearance for said line at said exchange; ah operator's position, and an emergency jack andline signal appearance for said line thereat, means associated. with said line responsive-to a" line closure at said station for extending said line to said normal appearance, emergency switching means at said station, and other means associated with said line responsive to operation of said emergency switching means'to transfer said line from said normal appearance to said emergencyj jack and line signal appearance. Q

GEORGE SANDALLS, J a. 

